Power conversion systems are used in a variety of applications in which electrical power must be converted from one form to another, such as supplying power to a grid, driving electric motors, etc. AC to DC converters are often employed for driving inverter type AC motor drives, with the front-end converter rectifying AC power from a utility or other supply to provide a DC bus to one or more inverters for driving AC motors or other loads. In many such rectifier systems, a pre-charge system is provided to control the DC bus voltage rise time so as to limit the inrush current into capacitive loads during power-up and to mitigate or avoid stressing system components. These objectives are hindered if the pre-charge system itself is damaged or inoperative. In addition, certain pre-charge circuit failure modes may adversely affect the steady state operation of the power converter. Troubleshooting the system using an oscilloscope or other external measuring devices via trial and error methods typically requires repeated power cycles of the AC line and often leads to additional stress on DC bus capacitors and other system components. The increased component stress during troubleshooting may result in other failures in the system and reduced component life. Accordingly, there is a need for techniques by which pre-charge problems can be diagnosed in AC to DC converters while mitigating the system down-time and component degradation.